Internal combustion engine producing low emissions

ABSTRACT

An engine is provided which includes various precise configuration parameters, including dimensions, shape and/or relative positioning of the combustion chamber features, resulting in a combustion process minimizing NOx emissions and particulates. The combustion chamber includes one or more of the following: a spray angle relative to an inner bowl floor angle; a vertical distance from the tip of the piston bowl to the injection orifices; a number of injection orifices; a swirl ratio; a vertical distance from the injection orifices to an inner face of the cylinder head; a radius of curvature of an outer bowl section; chamfer with dimensional parameters; and a transition radius.

This application is a continuation-in-part of application Ser. No.10/814,332, filed Apr. 1, 2004, the contents of which are incorporatedherein by reference, which is a continuation of application Ser. No.10/166,051, filed Jun. 11, 2002, now Pat. No. 6,732,703.

BACKGROUND OF THE INVENTION

1. Technical Field

The invention relates to an improved engine capable of minimizingemissions.

2. Description of the Related Art

Internal combustion engine designers continue to confront an ever moredemanding set of governmentally mandated emissions standards andperformance objectives. Modifications made to meet one standard may leadto increased emissions of a type that cause another standard to beexceeded. Thus designers are often confronted with not only thechallenge of meeting a newly imposed emission standard but to do so in away that does not cause other emissions standards, previously met ornewly imposed, to be exceeded. The engine designers must alsonecessarily consider and preferably minimize the adverse effects ofmodifications on engine performance and fuel economy.

An example of the difficulties created for engine designers is thatcreated by a new set of diesel engine emissions standards/limitsmandated by the Environmental Protection Agency for application in theU.S. market. These standards require diesel engines to produce extremelylow levels of emissions below specific limits based upon fuelconsumption. Specifically, for example, new on-highway regulationsrequire diesel engines complying with the regulations to maintainnitrogen oxide (NOx) emissions combined with unburned hydrocarbons below2.5 grams/b-hp-hr and particulates below 0.1 grams /b-hp-hr.

Changes in any one of a variety of engine design variables or engineoperating variables such as engine compression; combustion chambershape; rate of combustion chamber heat rejection and/or fuel injectionspray pattern, pressure, timing and/or flow rate may be used topositively affect the control of one or more emissions. However, suchchanges can often adversely affect one or more other emissions possiblycausing the emissions to exceed the acceptable limit. For example, asthe brake mean effective pressure (bmep) is desirably increased, atendency arises for NOx emissions in the engine's exhaust to increase.This problem is accentuated by the need to achieve other critical engineoperating characteristics such as fuel economy, high torque output, lowoperating costs and/or reduced maintenance. As one example, the amountof soot that is entrained in the engine's lubrication oil can have aprofound effect on the cost of operation and the length of servicebefore a major overhaul is required. Soot is very abrasive and can causehigh wear if allowed to become entrained in the engine's lubrication oilto any substantial degree. The amount of soot entrained in the engine'slubrication oil can be affected by a number of factors such ascombustion chamber shape and fuel injection spray angle but changes inthese variables can have the undesired effect of actually increasingemissions entrained in the engine's lubrication oil.

Many attempts have been made to produce an ideal flow pattern for thecharge air and fuel within the combustion chamber of an internalcombustion chamber. For example, provision of a combustion bowl in theupper region of a piston to cause, among other things, fuel/charge airmixture within a direct injection engine is well known as disclosed thearticle entitled “Future Developments . . . ”, Automotive Industries,Oct. 15, 1952. While most of the combustion bowl designs disclosed inthis article appear to be symmetric about a central axis, the articledoes not address the critical relationship of the combustion bowl shapeand the fuel injection path, nor other combustion chamber features, onthe specific problems addressed by the subject invention.

A variety of piston designs have been disclosed including symmetricalbowl shaped recesses formed in the upper surface of the piston crown toachieve desired flow patterns within the combustion chamber formed inpart by the piston. These bowl configurations are often referred to as“Mexican-hat” designs. For example, U.S. Pat. No. 4,377,967 discloses anarticulated piston assembly including a crown containing a symmetricalcombustion bowl in the top surface defined by a cone shaped centralfloor section which connects at its base to an arcuate surface ofrevolution coaxial with the central axis of the cone surface wherein thesurface of revolution flares upwardly to join with the uppermost surfaceof the piston. The base of the cone shaped central floor section extendsover no more than approximately 50% of the diameter of the bowl. Othersimilar piston designs are disclosed in U.K. Patent Application No.2,075,147; and U.S. Pat. Nos. 1,865,841; 3,508,531; 4,242,948 and5,029,563. However, none of these references disclose any critical sizeranges or ratios for the disclosed combustion bowl and chamber designs,suggest the importance of the angle of the fuel spray from the sprayorifices in relationship to the combustion bowl shape and specificdistances between the piston and both the cylinder head and sprayorifices. Thus, these patents fail to disclose that the combustionchamber and piston bowl have crucial dimensions and dimensionalrelationships that are required to achieve specific enginefunctionalities including low emissions.

U.S. Pat. No. 5,868,112, assigned to the assignee of the presentinvention, discloses a piston having a crown containing a combustionbowl shaped to complement the injection fuel spray plume in a manner tomaintain very low entrainment of soot in the lubrication oil of theengine and to maintain other engine emissions within acceptable ranges.However, this patent does not appreciate the specific combination offeatures and dimensions necessary to produce both NOx and particulatesbelow the new regulated limits.

U.S. Pat. No. 4,781,159 to Elsbett et al. discloses a composite pistonfor use in a cylinder of a diesel engine where the composite piston hasa crown with “Mexican-hat” design with additional features that enhancestrength and improve cooling of the piston. Various cross-sectionalfigures of the Elsbett et al. reference appear to show an angled chamferon the composite piston. However, this reference does not appreciate thesignificance of such a feature, the importance of the dimensionalparameters of the chamfer, or the specific combination of the chamfertogether with dimensions of other features of the piston which isnecessary to produce both NOx and particulates below the new regulatedlimits.

Despite the many examples of combustion chamber arrangements, includingpiston designs, contained in the prior art, the prior art does notappear to suggest an arrangement that creates the appropriatecooperation between the piston and an injector spray plume to minimizeNOx emissions while effectively promoting the oxidation of particulatesduring combustion by controlling and directing combustion gases in amanner to achieve acceptably low exhaust emissions relative to the newregulated limits. A need, thus, exists for an engine and combustionchamber arrangement that is capable of achieving this combination offunctionality.

SUMMARY OF THE INVENTION

It is, therefore, one object of the present invention to overcome thedeficiencies of the prior art and to provide an internal combustionengine containing a combustion chamber arrangement designed to reduceundesirable engine emissions sufficiently to meet new regulated limits.

Another object of the invention is to provide a combustion chamberarrangement which reduces undesirable engine emissions sufficiently tomeet new regulated limits while also minimizing soot in the enginelubrication oil and maintaining other engine performance requirements,such as fuel economy, at acceptable levels.

Still another object of the present invention is to provide a dieselengine capable of meeting the new NOx and particulate emissionregulations while maintaining acceptable fuel consumption and lube oilsoot contamination.

Another object of the present invention is to provide a diesel enginecapable of operating below 2.5 gramslb-hp-hr of NOx emissions plusunburned hydrocarbons and below 0.1 grams/b-hp-hr of particulates whilealso satisfying mechanical design constraints for a commerciallyacceptable engine.

A more specific object of the subject invention is to provide an engineincluding a combustion chamber arrangement having dimensions anddimensional relationships to minimize the amount of fuel exposed tooxygen in the chamber during the initial portion of the injection tominimize NOx emissions while ensuring oxidation of sufficientparticulates during combustion to minimize both particulates availablefor entrainment in the engine's lubrication oil and particulatesavailable for discharge to the exhaust system.

A still more specific object of the subject invention is to provide akey combination of combustion chamber design parameters that togetherresult in a combustion recipe that produces lower NOx emissions thanconventional engines.

According to the invention, the above objects and other more detailedobjects may be achieved by providing an engine with a combustion chamberarrangement having certain predetermined combinations of combustionchamber design parameters, including specific combustion chamberdimensions and dimensional relationships. For example, in the preferredembodiment, an internal combustion engine containing a combustionchamber is provided the engine comprising an engine body including anengine cylinder, a cylinder head forming an inner face of the combustionchamber and at least one intake port formed in the cylinder head fordirecting intake air into the combustion chamber. The engine alsoincludes a piston positioned for reciprocal movement in the enginecylinder between a bottom dead center position and a top dead centerposition, the piston including a piston crown including a top facefacing the combustion chamber, the piston crown containing a piston bowlformed by an outwardly opening cavity. In one embodiment, the pistonbowl includes a projecting portion having a distal end, an inner bowlfloor section extending inwardly, an outwardly flared outer bowl sectionhaving a concave curvilinear shape in cross section, and a chamferextending toward the top face at an angle δ in the range of 30 to 75degrees from an axis of reciprocation of the piston. An injector isfurther provided which is mounted on the engine body adjacent theprojecting portion of the piston bowl to inject fuel into the combustionchamber, the injector including a plurality of orifices arranged to forma spray plume.

In accordance with another embodiment of the present invention, theinner bowl floor section extends inwardly at an inner bowl floor angle αfrom a plane perpendicular to the axis of reciprocation of the piston,and each of the plurality of orifices have a central axis oriented at aspray angle β from a plane perpendicular to the axis of reciprocation ofthe piston, so that the spray angle β minus the inner bowl floor angle α(β−α) is in the range of −7 to 19.

In still another embodiment of the present invention, the chamferextends toward the top face a vertical distance K in the range of 1 to17 mm. In yet another embodiment, the piston bowl may include atransition radius R₄ between an end of the outer bowl section and thechamfer in the range of 1.5 to 7 mm. Moreover, in yet anotherembodiment, the plurality of orifices include an outlet opening having acenter, the center being a distance L₁ in the range of 0.5 to 12 mm fromthe distal end of the projecting portion.

In the above embodiments, the injector may have 8 or less orifices, anda distance L₂ between the center of the outlet opening and the innerface of the cylinder head forming the combustion chamber is in the rangeof −0.5 to 3 mm. In addition, the intake air preferably undergoes aswirling effect during operation to provide a swirl ratio in the rangeof 0.5-2.5. Moreover, the concave curvilinear shape of the outwardlyflared outer bowl section has a radius of curvature R₁ in the range of 8to 20 mm, and the distance BH between the top face of the piston crownand the center of the outlet opening is in the range of 0.5 to 8 mm.

Of course, other specific combinations of the design parameters taughtherein are also deemed to be within the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cutaway view of a portion of the internal combustion engineof the present invention employing the combustion chamber arrangement ofthe present invention with the piston in the top dead center position;

FIG. 2 is an enlarged view of a portion of FIG. 1 showing variousdimensions;

FIGS. 3 a-3 c are cutaway cross sectional views similar to FIG. 1showing sequentially the progress of the spray plume during an injectionevent as the piston moves from the top dead center position toward thebottom dead center position;

FIG. 4 is an enlarged cutaway, cross sectional view taken through theend of the injector nozzle assembly of FIG. 1 which contains theinjection orifices;

FIG. 5 is a graph illustrating normalize data showing the emissionsresults of the present invention relative to emissions levels of currentproduction engines;

FIG. 6 is a graph illustrating the effects of varying distance L₁ withthe engine of the present invention;

FIG. 7 is a graph illustrating normalized data showing the emissionsresults of the present engine relative to emissions levels of currentproduction engines;

FIG. 8 is an enlarged cutaway of a portion of an internal combustionengine employing the combustion chamber arrangement in accordance withanother embodiment of the present invention with the piston in the topdead center position; and

FIG. 9 is a schematic view of the piston bowl profile of FIG. 8 withdetails of the chamfer in accordance with one embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, the present invention is directed to an internalcombustion engine, a portion of which is shown in a cutaway crosssectional view and generally indicated at 10, capable of producingemissions, e.g. NOx and particulates, at levels significantly lower thanemissions levels produced by conventional engines and below recentgovernment regulated limits. As discussed hereinbelow, engine 10includes various precise configuration parameters resulting in acombustion process which achieves desired combustion characteristics forproducing acceptably low emissions satisfactory to meet newly adoptedengine operating standards applicable to diesel engines including bothlow noxious emissions and low particulates, while achieving desirablefuel economy and efficiency.

Engine 10 includes an engine block, only a small portion of which isillustrated at 12, and at least one combustion chamber 14. Of course,the engine may contain a plurality of combustion chambers, typicallyfour to eight, which may be arranged in a line or in a “V”configuration. Each combustion chamber is formed at one end of acylinder cavity 16 which may be formed directly in engine block 12. Thecylinder cavity 16 may be arranged to receive a removable cylinder liner18 which is only partially shown in FIG. 1. As is also common, one endof the cylinder cavity is closed by an engine cylinder head 20. Theengine 10 further includes a respective piston 22 mounted in acorresponding liner 18 associated with each combustion chamber. Althoughonly a top portion of piston 22 is shown in FIG. 1, piston 22 may be anytype of piston so long as it contains the features identifiedhereinbelow necessary for accomplishing the present invention. Forexample, piston 22 may be an articulated piston or a single piece pistondesign. The upper surface or top face of piston 22 cooperates with head20 and the portion of cylinder liner 18 extending between head 20 andpiston 22 to define combustion chamber 14. Although not specificallyillustrated, piston 22 is connected through a connecting rod to acrankshaft of the internal combustion engine which causes the piston toreciprocate along a rectilinear path within cylinder liner 18 as theengine crankshaft rotates. FIG. 1 illustrates the position of piston 22in a top dead center (TDC) position achieved when the crankshaft ispositioned to move the piston to the furthest most position away fromthe rotational axis of the crankshaft. In the conventional manner, thepiston moves from the top dead center position to a bottom dead center(BDC) position when advancing through intake and power strokes. Forpurposes of this disclosure, the words “outward” and “outwardly”correspond to the direction away from the engine crankshaft and thewords “inward” and “inwardly” correspond to the direction toward thecrankshaft of the engine or bottom dead center position of the piston.

Engine 10 of the present invention is a four-cycle compression ignition(diesel) engine employing direct injection of fuel into each combustionchamber of the engine. An intake passage 24 selectively directs intakeair into combustion chamber 14 by means of a pair of poppet valves 26,only one of which is illustrated in FIG. 1. Similarly, an exhaustpassage 28 selectively directs exhaust gas from combustion chamber 14 bymeans of a pair of exhaust poppet valves 30, only one of which isillustrated in FIG. 1. The opening and closing of valves 26 and 30 maybe achieved by a mechanical cam or hydraulic actuation system or othermotive system in carefully controlled time sequence with the reciprocalmovement of piston 22.

At the uppermost, TDC position shown in FIG. 1, piston 22 has justcompleted its upward compression stroke during which the charge airallowed to enter the combustion chamber 16 from intake passage 24 iscompressed thereby raising its temperature above the ignitiontemperature of the engine's fuel. This position is usually consideredthe zero position commencing the 720 degrees of rotation required tocomplete four strokes of piston 22. The amount of charge air that iscaused to enter the combustion chambers may be increased by providing apressure boost in the engine's intake manifold. This pressure boost maybe provided, for example, by a turbocharger, not illustrated, driven bya turbine powered by the engine's exhaust, or maybe driven by theengine's crankshaft.

Engine 10 also includes an injector 32 securely mounted in an injectorbore 34 for injecting fuel at very high pressure into combustion chamber14 when piston 22 is approaching, at or moving away from, the TDCposition. Injector 32 includes, at its inner end, an injector nozzleassembly 36 which is held to the remainder of the injector assembly, notillustrated, by a means of a nozzle retainer 38. Injector 32 includes aplurality of small injection orifices 40, formed in the lower end ofnozzle assembly 36 for permitting the high pressure fuel to flow fromthe nozzle cavity of injector 32 into the combustion chamber at a veryhigh pressure to induce thorough mixing of the fuel with the hightemperature, compressed charge air within combustion chamber 14. Itshould be understood that injector 32 may be any type of injectorcapable of injecting high pressure fuel through a plurality of injectororifices into combustion chamber 14 in the manner described hereinbelowwith respect to the spray angle of the fuel. For example, injector 32may be a closed nozzle injector or an open nozzle injector. Moreover,injector 32 may include a mechanically actuated plunger housed withinthe injector body for creating the high pressure during an advancementstroke of the plunger assembly. Alternatively, the injector 32 mayreceive high pressure fuel from an upstream high pressure source such asin a pump-line-nozzle system including one or more high pressure pumpsand/or a high pressure accumulator and/or a fuel distributor. Theinjector 32 may include an electronically actuated injection controlvalve which supplies high pressure fuel to the nozzle valve assembly toopen the nozzle valve element, or controls the draining of high pressurefuel from the nozzle valve cavity to create a pressure imbalance on thenozzle valve element thereby causing the nozzle valve element to openand close to form an injection event. For example, the nozzle valveelement 36 may be a conventional spring-biased closed nozzle valveelement actuated by fuel pressure, such as disclosed in U.S. Pat. No.5,326,034, the entire contents of which is hereby incorporated byreference. The injector 32 may be in the form of the injector disclosedin U.S. Pat. No. 5,819,704, the entire contents of which is herebyincorporated by reference.

The engine of the present invention includes combustion chambercomponents and features sized, shaped and/or positioned relative to oneanother, as described hereinbelow, to advantageously reduce both NOxemissions and particulates to levels at or below new regulatorystandards while maintaining acceptable fuel economy. Specifically, thedimensions, shape and/or relative positioning of the combustion chambercomponents and features reduce the exposure of the fuel to oxygen incombustion chamber 14 during the initial portion of an injection eventthereby reducing NOx emissions while ensuring sufficient oxidation ofparticulate matter later in the combustion event and minimizinginteraction between the combustion gases and the cylinder walls. Thedimensions, shape and/or relative positioning of the combustion chambercomponents and features as described hereinbelow results in a combustionchamber capable of forming, directing, controlling and creating apattern of injected fuel and gaseous flow within the combustion chamber14 during both the initial stages of fuel injection and during theinitiation of combustion and expansion of the resulting gases during thepower stroke of piston 22 so as to achieve optimum emission reductions.

To understand the unique physical characteristics of combustion chamber14, attention is initially directed to FIGS. 1 and 2 illustrating thevarious physical characteristics or parameters, at least two, andpreferably all, of which are required to achieve the unexpected emissionreduction advantages of the present invention. While the general shapeof the combustion chamber has antecedence in the prior art, it is thespecific configuration, and more importantly, the critical dimensionsand dimensional relationships described hereinbelow which result in theimproved functional performance of the present invention. Moreparticularly, the upper portion of piston 22 may be referred to as thepiston crown 50. This area of the piston includes a dependingcylindrical wall having a plurality of outwardly opening, annulargrooves 52 for receiving corresponding piston rings designed to form arelatively tight combustion gas seal between the piston and thesurrounding walls of cylinder liner 18. Piston crown 50 includes a topface 54 partially forming combustion chamber 14 and a piston bowl 56formed by an outwardly opening cavity. Piston bowl 56 includes aprojecting portion 58 preferably positioned at or near the center ofbowl 56. Projecting portion 58 includes a distal end 60 positioned, inthe preferred embodiment shown in FIG. 1, at the center of piston bowl56 and thus positioned along the axis of reciprocation of piston 22.Projecting portion 58 also includes an inner bowl floor section 62extending from projecting portion 58 inwardly (toward the BDC positionof piston 22) at an inner bowl floor angle α in the range of 16-40degrees from a plane perpendicular to an axis of reciprocation of piston22 as shown in FIG. 1. As will be explained hereinbelow, the inner bowlfloor angle α is designed to be relatively steep and also designedrelative to a spray angle β so as to cause desirable interaction betweena fuel spray pattern or plume 63 (FIG. 3 a) and piston bowl 56 necessaryfor optimized engine emissions reductions. Preferably, a more specificand desirable range for inner bowl floor angle α would be between 18 and30 degrees.

Piston bowl 56 also includes an outwardly flared outer bowl section 64having a generally concave curvilinear shape in diametric cross section.Outer bowl section 64 effectively shapes and directs the flow of fueland the fuel/air mixture within the combustion chamber. Outer bowlsection 64 is designed with a particular radius R₁ and a particularlocation for a center of radius CR₁ so as to ensure the spray plumeinteracts with an inner face 65 of cylinder head 20 in an appropriatemanner to ensure proper mixing and burning without interaction with thewalls of cylinder liner 18. Specifically, R₁ may range between 8 and 20mm, and preferably within the range of 12-16.5 mm. For each of thedimensional ranges provided herein, a value within the higher end of therange will likely be more appropriate for larger engines having largerpiston diameters and a value falling within the lower end of the rangewill more likely to be more desirable for smaller engines having smallerdiameter pistons. Also, the location of the center of radius CR₁ for R₁is preferably positioned on a plane extending through top face 54 ofpiston 22, or within piston bowl 56, and thus it is less desirable forR₁ to be positioned above top face 54 shown in FIG. 1. By combining themagnitude of R₁ and the location of CR₁ as described herein, the presentinvention creates outer bowl section 64 with an outward flare capable ofcontrolling the momentum of spray plume 63 as it follows outer bowlsection 64 to optimize combustion. An important objective of the subjectinvention is to minimize the amount of soot which actually reaches andbecomes entrained in the lubrication film formed on the cylinder wallsof liner 18 by promoting efficient combustion of the fuel withincombustion chamber 14 while creating and constraining the flow of gaseswithin the combustion chamber 14 to further minimize the possibility ofsoot entrainment within the film by ensuring the completeburning/oxidation of the particulates formed during the combustionprocess. Specifically, the position of CR₁ and the magnitude of R₁ensures that the spray plume and fuel/air mixture rolling off the upperedge 66 of bowl 56 has sufficient momentum to be directed into cylinderhead 20 resulting in the proper degree of mixing and oxidation ofparticulates. Outer bowl section 64 is specifically designed to preventinadequate momentum of the spray plume and fuel/air mixture which wouldcause undesirable stagnation of the plume and air fuel mixture withoutinteraction with the cylinder head thereby resulting in inadequatemixing and burning of particulates. This is achieved by having an R₁that is sufficiently large resulting in a curvature in outer bowlsection 64 to create and maintain the momentum in the spray plume andfuel/air mixture. Outer bowl section 64 is also designed to preventexcessive momentum in the spray plume and fuel/air mixture which wouldcause the spray plume and fuel/air mixture to interact with the cylinderhead with an excessive velocity causing the spray plume/fuel/air mixtureto impact cylinder head 20 and spread or rebound toward the cylinderwalls formed by cylinder liner 18. The fuel interacting with the lubeoil film on the cylinder walls of combustion chamber 14 causes theunburned particulates in the fuel/air mixture to become entrained withinthe lubrication film resulting in soot which eventually works its waybelow the piston rings where it may become intermixed with the enginelubrication oil. The amount of fuel and particulates interacting withoil on the cylinder wall is at least partially minimized by using an R₁that is sufficiently small to create a curvature which avoids excessivemomentum in the spray plume and fuel/air mixture. Thus, R₁ is designedto modulate the momentum of the combustion plume to ensure the plume hassufficient momentum to interact with the cylinder head and reflect backinto the open space of the combustion chamber 14. Decreasing R₁ tends todecrease the momentum of the combustion plume.

The upper surface of outer bowl section 64 adjacent edge 66 preferablyextends vertically parallel to the axis of the piston, or slightlyinward toward the axis of reciprocation of piston 22. That is, if thisupper surface of outer bowl section 64 at edge 66 has a center of radiusCR₁ then CR₁ is preferably positioned on a plane extending through topface 54 or positioned with bowl 56. The curvilinear shape of outer bowlsection 64 may be formed by a surface having a radius of curvature R₁which terminates before edge 66 while a vertical upper portion of outerbowl section 64 extends tangentially from the surface having a radius ofcurvature R₁, vertically to edge 66. Preferably, as noted above, CR₁ isnot positioned above top face 54, and preferably the upper portion ofouter bowl section 64 adjacent edge 66 does not intersect edge 66 in amanner which directs gases outwardly toward the cylinder walls formed bycylinder liner 18. In this manner, proper control of the spray plume andfuel/air mixture and control of the interaction with the cylinder headis enhanced while preventing interaction with the cylinder walls therebyminimizing emissions and reducing soot.

As shown in FIG. 3, spray or injection orifices 40 of injector 32 extendthrough the injector nozzle 36 to deliver fuel to combustion chamber 14.An important aspect of the subject invention involves orienting thecentral axis of each orifice 40 in a relatively steep spray angle βmeasured between a plane perpendicular to the axis of reciprocation ofthe piston and a central axis of each spray orifice 40 (FIGS. 1 and 4).Therefore, β is the angle of spray emanating from fuel injectionorifices 40. Spray angle β may be equal to a value causing the sprayangle β minus the inner bowl floor angle α to be in the range of 0-19degrees, but preferably within the range of 1-13 degrees. Thisdimensional relationship results in the fuel spray plume 63 beingdirected toward the upper portion of projecting portion 58 near theupper edge of inner bowl floor section 62 as shown in FIG. 3 a. Althoughit is possible that the fuel spray may be directed in a paralleldirection along inner bowl floor section 62 under certain conditionswhere the movement of piston 22 and swirling of the air causes the sprayplume to be forced into impingement with inner bowl floor section 62,preferably the central axis of the spray plume 63, which is also thecentral axis of each spray orifice 40 passing through the center C ofeach outlet opening 68 (FIG. 4) of each spray orifice 40, is angledslightly toward inner bowl floor section 62 at some angle such as anydegree greater than 0 and less than 13 degrees. As a result, spray plume63 engages projecting portion 58 soon after exiting outlet opening 68and spreads out over inner bowl floor section 62 of projecting portion58 as it flows downwardly as shown in FIGS. 3 a-3 c. By forming α and βsuch that the dimensional relationship between β and α, i.e. β minus α,causes spray plume 63 to be directed toward the top portion ofprojecting portion 58, the present invention maximizes the amount offuel in contact with inner bowl floor section 62 thereby minimizing theexposure of the fuel to oxygen in the combustion chamber 14 during theinitial portion of the injection event/combustion. As a result, theformation of NOx and particulate emissions is desirably minimized. FIG.5 illustrates normalized data showing the emissions results of thepresent invention at β−α=8 degrees relative to emissions levels ofcurrent production engines. FIG. 5 illustrates that key benefit of thepresent invention in reducing both NOx and particulate emissions, notjust one type of emissions.

Another important combustion chamber parameter of the present inventioncritical to ensuring that fuel spray plume 63 contacts projectingportion 58 quickly and properly interacts with inner bowl floor section62 is the vertical distance L₁ from the distal end 60 of projectingportion 58 to the center C of outlet openings 68 of injection orifices40 as shown in FIG. 2. The combustion chamber arrangement of the presentinvention specifically includes the dimension L₁ having a magnitude inthe range of 0.5-4 mm, and preferably in the range of 1.5-3 mm. An L₁value within this range has been found by applicants to effectivelyenhance and ensure the interaction of spray plume 63 with inner bowlfloor section 62 and minimize the length of the flow path of spray plume63 between the outlet opening 68 and the impingement point of the sprayagainst inner bowl floor section 62 thereby minimizing the opportunityfor oxidation of the fuel and thus minimizing NOx emissions. Also, witheach data point representing a different injection timing, a greaterdistance L₁, for the arrangement illustrated in FIG. 1, results insignificantly increased NOx emissions and decreased particulates asshown in FIG. 6.

Another important combustion chamber parameter significantly affectingemissions is the number N of injection or spray orifices 40. Inaccordance with the present invention, no more than six injectionorifices are used to deliver fuel to combustion chamber 14. Preferably,less than six injection orifices, such as four or five, are used. Thenumber of injection orifices N is critical for the following reason. Oneobject of the present invention is to minimize NOx emissions byminimizing the exposure of fuel to air in the combustion chamber duringthe initial portion of the injection event/combustion as the spray plumetravels from outlet openings 68 of injection orifices 40 to inner bowlfloor section 62. The greater the number of injection orifices, thegreater the number of spray plumes flowing through the combustionchamber resulting in a larger surface area of fuel exposed to oxygen inthe combustion chamber. Thus, the amount of fuel exposed to oxygen inthe combustion chamber can be reduced by reducing the number ofinjection orifices. However, this reduction in injection orifices mustbe balanced with the need to promote proper distribution of the fuelwithin combustion chamber 14 and effective mixing of the fuel and airduring the entire combustion process. Although many conventionalinjectors use more than six injection orifices, applicants have foundthat preferably no more than six orifices would be used and preferablyfour or five to minimize the exposure of the fuel to oxygen as ittravels toward inner bowl floor section 62 and as it flows across thevarious surfaces of bowl 56 thereby reducing NOx emissions.

Another important combustion chamber parameter beneficial in controllingemissions is the swirl ratio of the air flow that is generated by theintake ports 24. The swirl ratio SR is a ratio of the tangentialvelocity of the air spinning around combustion chamber 14 divided by theengine speed. That is, the swirl ratio is a measure of the tangentialmotion of the air as it enters the engine cylinder from the intakeport(s) of the cylinder head. Precisely, the term swirl ratio refers tothe average in-cylinder angular velocity of the air at intake valveclosing divided by the cylinder piston angular velocity. For example, anengine running at 1800 rpm with a head generating an air motion with aswirl ratio of 2 implies that the air in the cylinder at intake valveclosing is rotating with an average angular velocity of 3600 rpm. Thehigher the swirl ratio, the greater the swirling effect of the air orair fuel mixture, while the lower the swirl ratio, the lower theswirling effect. The swirling effect is a generally tangential motionthat upon compression by piston 22 creates turbulence and assists in thecombustion process. However, an increased swirling effect or swirl ratiogenerally tends to increase NOx emissions. The reason for this increasein NOx emissions is that the swirling effect tends to undesirablydeflect the plume and cause a decay in the momentum of the combustionplume exiting the piston bowl. As a result, the ability of the plume toexit the piston bowl and desirably interact with the combustion head(FIG. 3 c) is disadvantageously impeded possibly causing the plume toremain in the piston bowl thereby hindering complete combustion bypreventing maximum exposure to free oxygen. Applicants have found thatmaintaining a swirl ratio in the range of 0.5-2.5, and preferably withinthe range of 0.7-1.5, in combination with one or more of the othercombustion chamber parameters, maintains the swirling effect at asufficiently low level to enhance the reduction in NOx emissions whilestill permitting sufficient turbulence for combustion. By maintaining aswirl ratio within the preferred range, the combustion plume ispermitted to advantageously interact with the cylinder head (FIG. 3 c)to optimize exposure to free oxygen in the combustion chamber therebyenhancing the reductions in particulates and NOx emissions.

Another combustion chamber parameter which can be set to assist inreducing emissions is the vertical distance L₂ from the center C of theoutlet openings 68 of injection orifices 40 to the inner face 65 ofcylinder head 20 facing combustion chamber 14. That is, L₂ representsthe distance the injection orifices 40 protrude into the combustionchamber below cylinder head 20. Applicants have found that the range ofL₂ should preferably be −0.5-3 mm, wherein the negative value of L₂occurs when the center C of the outlet opening 68 is positioned justinside of the bore 34 of cylinder head 20.

Another important combustion chamber parameter is the distance BH fromthe piston top face 54 to the inner face of cylinder head 20 when piston22 is in the top dead center position as shown in FIG. 2. Applicantshave found that the preferred range for BH is 0.5-8 mm. Of course, thelower end of the BH value is limited by mechanical clearance issueswhile the important upper limit assists in confining the combustiongases more to the interior of the combustion chamber or piston, i.e. thepiston bowl 56. Applicants have found that BH significantly affects theinteraction of the combustion plume with the cylinder head. Also, it hasbeen found that a BH outside the preferred range is more likely toincrease soot in the lubrication oil on the cylinder walls. BH isespecially effective in combination with one or more of the othercombustion chamber parameters discussed herein to enhance the reductionsin emissions. It should be noted that the top face 54 of piston 22 isconsidered the outer most surface of the piston and therefore BH is notmeasured from a recessed surface such as those surfaces formed by valvepockets for providing clearance from open intake and exhaust valves.

Another critical combustion chamber parameter is the radius of curvatureR₂ at the lip or edge 66 of combustion bowl 56 as shown in FIG. 2.Although the radius R₂ is only shown at FIG. 2 at one point along edge66, it should be understood that R₂ is formed along the entire edge 66around the circumference of piston bowl 56. R₂ is preferably in therange of 0.5-1.5 mm. The upper limit of 1.5 mm is important tomaintaining the control over the direction of flow of the combustionplume as it flows off of outer bowl section 64. Applicants have foundthat an R₂ having a greater value than approximately 1.5 mm undesirablypermits a significant amount of combustion gases to flow toward thecylinder walls of liner 18 thereby undesirably increasing the level ofparticulates/soot developed in the lube oil film on the cylinder wall.Moreover, a smaller radius R₂ at edge 66 permits more control over thedirection of flow of the combustion gas in the vertical direction towardcylinder head 20 and thus ensures a continuation of the momentum anddesired interaction with the cylinder head, i.e. reflecting back intothe free air space of the combustion chamber in a desirable manner. Theobjective is to form R₂ with the smallest radius possible whilemaintaining the structural integrity of the piston.

Finally, the size of combustion chamber 14 can be adjusted to controlemissions. The cylinder bore diameter CD is preferably in the range of95-140 mm. The precise cylinder bore diameter within this range dependsgreatly on the desired size and power output of the engine. Similarly,the piston bowl diameter BD shown in FIG. 1 is preferably of a magnitudethat causes the ratio of the bowl diameter to the cylinder bore diameterBD/CD to be in the range of 0.5-0.9. Essentially, applicants had foundthat it is beneficial to form a BD/CD ratio which is as high as thestructural limits of the piston permit. Applicants have found that alarger piston bowl diameter BD improves fuel economy by exposing more ofthe combustion plume to more free oxygen after the initial bum as theplume interacts with the cylinder head (FIG. 3 c) resulting in improvedcombustion. Thus, applicants have found it to be very beneficial toachieve a BD/CD ratio between 0.8-0.9.

Combinations of the above described combustion chamber parametersselected within the specified ranges provided advantages in reducingemissions in comparison to conventional engine designs, includingspecifically meeting new emissions standards relative to NOx emissionsand particulates, and also in reducing lube oil contamination byparticulates. Combustion chamber 14 specifically includes a spray angleβ relative to an inner bowl floor angle α that maximizes the amount offuel in contact with the inner bowl floor section 62, in combinationwith one or more of the following dimensions and dimensionalrelationships hereinabove with respect to: the vertical distance L₁ fromthe distal end 60 of the piston bowl 56 to the center C of the outletopenings 68 of the injection orifices 40; the number N of injectionorifices; the swirl ratio SR; the vertical distance L₂ from theinjection orifices 40 to an inner face 65 of the cylinder head 20; thedistance BH from the piston top face 54 to cylinder head 20; the radiusof curvature R₁ of an outer bowl section 64; a radius of curvature R₂ atan edge of piston bowl 56; the ratio BD/CD of the piston bowl diameterto the cylinder diameter; and the cylinder diameter CD. FIG. 7illustrates normalized data showing the emissions results of the presentinvention relative to emissions levels of current production engines.For example, the data point farthest to the left on the graph shows thatwith the right combinations of the engine parameters as discussedhereinabove, diesel particulate matter can be reduced to approximately36% of the level typically produced by a conventional diesel productionengine, while NOx was reduced to approximately 62% of typicalconventional diesel engine levels. Thus, the NOx vs DPM tradeoff curveis radically different from a conventional engine in that both the NOxand particulates can be reduced simultaneously to levels withinregulated standards.

FIGS. 8 and 9 show a piston bowl 156 in accordance with anotherembodiment of the present invention, FIG. 8 showing a partial cutaway ofa portion of a combustion chamber for internal combustion engine 100,while FIG. 9 shows a partial schematic view of the piston bowl profileof FIG. 8. The piston bowl 156 of engine 100 is optimized for injectornozzle 140 in which the number of injection orifices N is eight or less.Thus, whereas the previously described piston bowl profile discussedabove relative to FIGS. 1 and 2 were optimized for injector nozzles withsix or less injection orifices, the present piston bowl profile ofengine 100 allows for higher number of injection orifices.

In the illustrated implementation, some of the various parametersdiscussed above still apply. In this regard, various parameters of theengine 100 corresponds to the engine 10 discussed above, and thus, FIGS.1, 2, and 4 apply in defining such parameters with respect to engine100. The swirl ratio SR of engine 100 is maintained in the range of 0.5to 2.5, and is preferably within the range of 0.7 to 1.5 in theillustrated embodiment. The swirl ratio SR, in combination with one ormore of the other combustion chamber parameters described in furtherdetail below, maintains the swirling effect at a sufficiently low levelto enhance the reduction in particulates and NOx emissions where theinjector nozzles 140 are implemented with eight or less injectionorifices.

In addition, the vertical distance L₂ from the center C of the outletopenings of injection orifices 140 to the inner face 165 of cylinderhead 120, which represents the distance the injection orifices 140protrude into the combustion chamber below cylinder head 120, is in therange of −0.5 to 3 mm. The outer bowl section 164 of the illustratedpiston bowl 156 has radius R₁ in a range between 8 and 20 mm, andpreferably, within the range of 12 to 16.5 mm. This radius R₁ ensuresthat the spray plume interacts with an inner face 165 of cylinder head20 in an appropriate manner to ensure proper mixing. In particular, theradius of curvature R₁ of the outer bowl section 164 is optimized tomodulate the amount of time required for the combustion plume to movealong the contoured surface, the contour of the piston bowl 156 helpingto redirect the combustion plume. The time required for the combustionplume to move along the bottom contour of the piston bowl 156 isincreased as the radius is decreased, correspondingly slowing down thecombustion which results in lower NOx emissions.

Moreover, the distance BH from the piston top face 154 to the inner face165 of cylinder head 20 when piston 122 is in the top dead centerposition is preferably in the range of 0.5 to 8 mm. As describedpreviously, applicants have found that BH significantly affects theinteraction of the combustion plume with the cylinder head, and that aBH outside the preferred range is more likely to increase soot in thelubrication oil on the cylinder walls.

The piston bowl 156 of engine 100 shown in FIGS. 8 and 9 relies on thecombustion plume contact with the piston bowl surface to help controlnitrous oxide emissions. By optimization of the spray angle β and thebowl floor angle α, the combustion plume contacts the piston 122 asillustrated in FIG. 8. Correspondingly, the combustion plume thatimpinges on the piston bowl 156 reduces the amount of hot gases, andreduces the amount of diffusion flame surface area which contributes toNOx emissions formation. In this regard, in the piston bowl 156 of theengine 100 shown, the dimensional relationship between the bowl floorangle α and the spray angle β is such that β minus α is between −7 to 19degrees (β−α=−7 to 19), the negative angle occurring when the sprayangle β is less than the bowl floor angle α. Thus, in contrast to theembodiment of the present invention described relative to FIGS. 1 and 2,the piston bowl 156 of combustion chamber 100 may be implemented suchthat there is reduced impingement of the injected fuel on the inner bowlfloor section 162.

In addition, in the engine 100 of FIGS. 8 and 9, the vertical distanceL₁ from the distal end 160 of projecting portion 158 to the center C ofthe outlet openings of injection orifices 140 is optimized so that L₁ isin the range of 0.5 to 12 mm, which is substantially larger than therange of 0.5 to 4 mm for the previously described embodiment of FIGS. 1and 2. The vertical distance L₁ from the distal end 160 of projectingportion 158 to the center C of the outlet openings of injection orifices140 is increased to prevent excessive liquid fuel from impinging on thepiston crown 150, such impingement of liquid fuel being caused in part,by unburned fuel and carbon particulates.

Correspondingly, to minimize the formation of NOx and particulateemissions, the piston bowl 156 of engine 100 is provided with a chamfer170 that is defined by various parameters δ, R₄, and K which arediscussed in detail below. Referring to FIG. 8, it should be evidentthat the chamfer 170 is provided at the end of the outer bowl section164, the chamfer 170 extending upwardly toward the top face 154 of thepiston 122.

As most clearly shown in FIG. 9, the end of the outer bowl section 164transitions to the chamfer 170 at transition radius R₄. The transitionradius R₄ is preferably in the range of approximately 1.5 to 7 mm. Thechamfer 170 is angled δ in the range of approximately 30 to 75 degreesfrom the axis of reciprocation of the piston 122 toward the top face 154of the piston 122 and terminates at the top face 154. In addition, thechamfer 170 extends approximately a distance K in the range ofapproximately 1 to 17 mm toward the top face 154 of the piston 122 andterminates at the top face 154.

The above described chamfer 170 provided in the piston bowl 156 ofengine 100 as shown in FIGS. 8 and 9, reduces the likelihood of thecombustion plume from separating from the piston bowl 156, andcontacting the cylinder head 120. The illustrated piston bowl profileallows a portion of the combustion plume to remain in contact with thepiston bowl 156 which allows further reduction in NOx emissions. Thefuel injection timing can then be adjusted to achieve a more fuelefficient thermodynamic cycle which results in better fuel economy at aprescribed NOx value. In addition, the described chamfer 170 providesless heat flux to the cylinder head 120. Furthermore, the chamfer 170reduces particulate matter that is confined to the region along the topof the cylinder head 120 so as to reduce the likelihood of poorparticulate oxidation which may occur when soot is confined near thecylinder head 120 due to the lack of available oxygen.

While various embodiments in accordance with the present invention havebeen shown and described, it is understood that the invention is notlimited thereto. The present invention may be changed, modified andfurther applied by those skilled in the art. Therefore, this inventionis not limited to the detail shown and described previously, but alsoincludes all such changes and modifications.

INDUSTRIAL APPLICABILITY

It is understood that the present invention is applicable to allreciprocating piston internal combustion engines. This invention isparticularly applicable to diesel engines and specifically heavy dutydiesel engines, used in truck and automotive vehicles as well asindustrial applications, for example stationary power plants and others.

1. An internal combustion engine containing a combustion chamber,comprising: an engine body including an engine cylinder, a cylinder headforming an inner face of the combustion chamber and at least one intakeport formed in the cylinder head for directing intake air into thecombustion chamber; a piston positioned for reciprocal movement in saidengine cylinder between a bottom dead center position and a top deadcenter position, said piston including a piston crown including a topface facing the combustion chamber, said piston crown containing apiston bowl formed by an outwardly opening cavity, said piston bowlincluding a projecting portion having a distal end, an inner bowl floorsection extending inwardly, an outwardly flared outer bowl sectionhaving a concave curvilinear shape in cross section, and a chamferextending toward said top face at an angle δ in the range of 30 to 75degrees from an axis of reciprocation of the piston; and an injectormounted on the engine body adjacent said projecting portion of saidpiston bowl to inject fuel into the combustion chamber, said injectorincluding a plurality of orifices arranged to form a spray plume.
 2. Theengine of claim 1, wherein said inner bowl floor section extendsinwardly at an inner bowl floor angle α from a plane perpendicular tothe axis of reciprocation of the piston, and each of said plurality oforifices have a central axis oriented at a spray angle β from a planeperpendicular to the axis of reciprocation of the piston, so that saidspray angle β minus said inner bowl floor angle α (β−α) is in the rangeof −7 to
 19. 3. The engine of claim 1, wherein said chamfer extendstoward said top face a vertical distance K in the range of 1 to 17 mm.4. The engine of claim 1, wherein said piston bowl further includes atransition radius R₄ between an end of said outer bowl section and saidchamfer in the range of 1.5 to 7 mm.
 5. The engine of claim 1, whereineach of said plurality of orifices include an outlet opening having acenter, said center being a distance L₁ in the range of 0.5 to 12 mmfrom said distal end of said projecting portion.
 6. The engine of claim1, wherein said plurality of orifices are no more than 8 orifices. 7.The engine of claim 1, wherein the intake air undergoes a swirlingeffect during operation to provide a swirl ratio in the range of0.5-2.5.
 8. The engine of claim 1, wherein a distance L₂ between saidcenter of said outlet opening and said inner face of said cylinder headforming said combustion chamber is in the range of −0.5 to 3 mm.
 9. Theengine of claim 1, wherein said concave curvilinear shape of saidoutwardly flared outer bowl section has a radius of curvature R₁ in therange of 8 to 20 mm.
 10. The engine of claim 1, wherein a distance BHbetween the top face of the piston crown and said center of said outletopening is in the range of 0.5 to 8 mm.
 11. An internal combustionengine containing a combustion chamber, comprising: an engine bodyincluding an engine cylinder, a cylinder head forming an inner face ofthe combustion chamber and at least one intake port formed in thecylinder head for directing intake air into the combustion chamber; apiston positioned for reciprocal movement in said engine cylinderbetween a bottom dead center position and a top dead center position,said piston including a piston crown including a top face facing thecombustion chamber, said piston crown containing a piston bowl formed byan outwardly opening cavity, said piston bowl including a projectingportion having a distal end, an inner bowl floor section extendinginwardly, an outwardly flared outer bowl section having a concavecurvilinear shape in cross section, a chamfer extending at an angletoward said top face, and a transition radius R₄ between end of saidouter bowl section and said chamfer in the range of 1.5-7 mm; and aninjector mounted on the engine body adjacent said projecting portion ofsaid piston bowl to inject fuel into the combustion chamber, saidinjector including a plurality of orifices arranged to form a sprayplume.
 12. The engine of claim 11, wherein said inner bowl floor sectionextends inwardly at an inner bowl floor angle α from a planeperpendicular to an axis of reciprocation of the piston, and each ofsaid plurality of orifices have a central axis oriented at a spray angleβ from a plane perpendicular to the axis of reciprocation of the piston,so that spray angle β minus said inner bowl floor angle α (β−α) is inthe range of −7 to
 19. 13. The engine of claim 11, wherein said chamferextends toward said top face a vertical distance K in the range of 1 to17 mm.
 14. The engine of claim 11, wherein said piston bowl furtherincludes a transition radius R₄ between end of said outer bowl sectionand said chamfer in the range of 1.5 to 7 mm.
 15. The engine of claim11, wherein each of said plurality of orifices include an outlet openinghaving a center, said center being a distance L₁ in the range of 0.5 to12 mm from said distal end of said projecting portion.
 16. The engine ofclaim 11, wherein said plurality of orifices are no more than 8orifices.
 17. The engine of claim 11, wherein the intake air undergoes aswirling effect during operation to provide a swirl ratio in the rangeof 0.5-2.5.
 18. The engine of claim 11, wherein a distance L₂ betweensaid center of said outlet opening and said inner face of said cylinderhead forming said combustion chamber is in the range of −0.5 to 3 mm.19. The engine of claim 11, wherein said concave curvilinear shape ofsaid outwardly flared outer bowl section has a radius of curvature R₁ inthe range of 8 to 20 mm.
 20. The engine of claim 11, wherein a distanceBH between the top face of the piston crown and said center of saidoutlet opening is in the range of 0.5 to 8 mm.
 21. An internalcombustion engine containing a combustion chamber, comprising: an enginebody including an engine cylinder, a cylinder head forming an inner faceof the combustion chamber and at least one intake port formed in thecylinder head for directing intake air into the combustion chamber; apiston positioned for reciprocal movement in said engine cylinderbetween a bottom dead center position and a top dead center position,said piston including a piston crown including a top face facing thecombustion chamber, said piston crown containing a piston bowl formed byan outwardly opening cavity, said piston bowl including a projectingportion having a distal end, an inner bowl floor section extendinginwardly, an outwardly flared outer bowl section having a concavecurvilinear shape in cross section, and a chamfer extending toward saidtop face a vertical distance K in the range of 1 to 17 mm; and aninjector mounted on the engine body adjacent said projecting portion ofsaid piston bowl to inject fuel into the combustion chamber, saidinjector including a plurality of orifices arranged to form a sprayplume.
 22. The engine of claim 21, wherein said inner bowl floor sectionextends inwardly at an inner bowl floor angle α from a planeperpendicular to an axis of reciprocation of the piston, and each ofsaid plurality of orifices have a central axis oriented at a spray angleβ from a plane perpendicular to the axis of reciprocation of the piston,so that spray angle β minus said inner bowl floor angle α (β−α) is inthe range of −7 to
 19. 23. The engine of claim 21, wherein each of saidplurality of orifices include an outlet opening having a center, saidcenter being a distance L₁ in the range of 0.5 to 12 mm from said distalend of said projecting portion.
 24. The engine of claim 21, wherein saidplurality of orifices are no more than 8 orifices.
 25. The engine ofclaim 21, wherein the intake air undergoes a swirling effect duringoperation to provide a swirl ratio in the range of 0.5-2.5.
 26. Theengine of claim 21, wherein a distance L₂ between said center of saidoutlet opening and said inner face of said cylinder head forming saidcombustion chamber is in the range of −0.5 to 3 mm.
 27. The engine ofclaim 21, wherein said concave curvilinear shape of said outwardlyflared outer bowl section has a radius of curvature R₁ in the range of 8to 20 mm.
 28. The engine of claim 21, wherein a distance BH between thetop face of the piston crown and said center of said outlet opening isin the range of 0.5 to 8 mm.
 29. An internal combustion enginecontaining a combustion chamber, comprising: an engine body including anengine cylinder, a cylinder head forming an inner face of the combustionchamber and at least one intake port formed in the cylinder head fordirecting intake air into the combustion chamber; a piston positionedfor reciprocal movement in said engine cylinder between a bottom deadcenter position and a top dead center position, said piston including apiston crown including a top face facing the combustion chamber, saidpiston crown containing a piston bowl formed by an outwardly openingcavity, said piston bowl including a projecting portion having a distalend, an inner bowl floor section extending inwardly at an inner bowlfloor angle α from a plane perpendicular to an axis of reciprocation ofthe piston, an outwardly flared outer bowl section having a concavecurvilinear shape in cross section, and a chamfer extending toward saidtop face; and an injector mounted on the engine body adjacent saidprojecting portion of said piston bowl to inject fuel into thecombustion chamber, said injector including a plurality of orificesarranged to form a spray plume, each of said plurality of orificeshaving a central axis oriented at a spray angle β from a planeperpendicular to the axis of reciprocation of the piston so that sprayangle β minus inner bowl floor angle α (β−α) is in the range of −7 to19.
 30. The engine of claim 29, wherein said chamfer extends at an angleδ in the range of 30 to 75 degrees from the axis of reciprocation of thepiston toward said top face.
 31. The engine of claim 30, wherein saidchamfer extends a vertical distance K in the range of 1 to 17 mm towardsaid top face.
 32. The engine of claim 31, wherein said piston bowlfurther includes a transition radius R₄ between end of said outer bowlsection and said chamfer in the range of 1.5 to 7 mm.
 33. The engine ofclaim 29, wherein each of said plurality of orifices include an outletopening having a center, said center being a distance L₁ in the range of0.5 to 12 mm from said distal end of said projecting portion.
 34. Theengine of claim 29, wherein said plurality of orifices are no more than8 orifices.
 35. The engine of claim 29, wherein the intake air undergoesa swirling effect during operation to provide a swirl ratio in the rangeof 0.5-2.5.
 36. The engine of claim 29, wherein a distance L₂ betweensaid center of said outlet opening and said inner face of said cylinderhead forming said combustion chamber is in the range of −0.5 to 3 mm.37. The engine of claim 29, wherein said concave curvilinear shape ofsaid outwardly flared outer bowl section has a radius of curvature R₁ inthe range of 8 to 20 mm.
 38. The engine of claim 29, wherein a distanceBH between the top face of the piston crown and said center of saidoutlet opening is in the range of 0.5 to 8 mm.
 39. An internalcombustion engine containing a combustion chamber, comprising: an enginebody including an engine cylinder, a cylinder head forming an inner faceof the combustion chamber and at least one intake port formed in thecylinder head for directing intake air into the combustion chamber; apiston positioned for reciprocal movement in said engine cylinderbetween a bottom dead center position and a top dead center position,said piston including a piston crown including a top face facing thecombustion chamber, said piston crown containing a piston bowl formed byan outwardly opening cavity, said piston bowl including a projectingportion having a distal end, an inner bowl floor section extendinginwardly, an outwardly flared outer bowl section having a concavecurvilinear shape in cross section, and a chamfer extending toward saidtop face; and an injector mounted on the engine body adjacent saidprojecting portion of said piston bowl to inject fuel into thecombustion chamber, said injector including a plurality of orificesarranged to form a spray plume, each of said plurality of orificeshaving a central axis and including an outlet opening having a center,said center being a distance L₁ in the range of 0.5 to 12 mm from saiddistal end of said projecting portion.
 40. The engine of claim 39,wherein said plurality of orifices are no more than 8 orifices.
 41. Theengine of claim 39, wherein the intake air undergoes a swirling effectduring operation to provide a swirl ratio in the range of 0.5-2.5. 42.The engine of claim 39, wherein a distance L₂ between said center ofsaid outlet opening and said inner face of said cylinder head formingsaid combustion chamber is in the range of −0.5 to 3 mm.
 43. The engineof claim 39, wherein said concave curvilinear shape of said outwardlyflared outer bowl section has a radius of curvature R₁ in the range of 8to 20 mm.
 44. The engine of claim 39, wherein a distance BH between thetop face of the piston crown and said center of said outlet opening isin the range of 0.5 to 8 mm.